INTERMITANT START PROBLEM.

1986 Nissan Pathfinder

My Nissan has trouble starting up sometiimes. When I turn the key, I hear a click and then nothing. To get to to start I have to take the shifter (the thing with N P D R 1 2 ON IT) AND SHIFT IN TO ALL THE POSITIONS TO GET THE CAR TO START. WHATS WRONG WITH MY CAR. 170000 mi V6